This application relates to substrate processing equipment including semiconductor manufacturing equipment, display panel manufacturing equipment and solar panel manufacturing equipment. More particularly, the application relates to improving defect levels of substrate processing equipment.
Substrate processing techniques are sensitive to contamination originating from the interior walls of processing chambers. The walls of pipes and elements of gas handling systems, gas exhaust systems and pumping systems are also sources of particulates and contaminants which may affect the performance of devices formed on substrate surfaces. Particulates which migrate to the substrate surface can interfere with the physical formation of vias, lines, transistors, diodes and other features on a substrate surface. A transfer of contaminants may also result in a change of dopant concentration or metal contamination which can adversely affect the performance of transistors and diodes by altering, even slightly, the chemical composition of the substrate or layers formed on the substrate.
The mobility of particulates and contamination from the interior walls of a substrate processing system is affected by the types of process gases used to process the substrate. Some processes use chlorine containing compounds which are chemically aggressive, reacting with the surfaces of the processing system. Aluminum on or near an exposed surface inside a processing system, for example, may be attacked by hydrogen chloride (HCl) which is a common effluent in, e.g., epitaxial (EPI) deposition systems.
Stainless steel of various types is used for many parts of substrate processing equipment. One type which is commonly found in processing systems is 316L stainless steel due, in part, to a resistance to chlorine corrosion. 316L stainless steel also forms cleaner welds which are more conducive to incorporation in processing equipment.
A primary component of stainless steel is iron (Fe), which can adversely affect substrate processing because the iron oxides are unstable in the presence of HCl. Electropolishing the exposed surfaces of 316L stainless steel results in a reduction in iron content and an improvement in surface smoothness. Some iron remains near the surface. Once the chamber is assembled, the chamber can be seasoned to further reduce the iron. Seasoning involves flowing process gases or process reaction by-products through various regions. For example, flowing HCl through the exhaust system removes additional iron from the surface and near-surface regions of the exposed surfaces of tubes and other components.
Components may also be coated with polymers to cover potential metal contaminants which may otherwise transfer to the substrate surface under process conditions. Coating films such as Teflon (PTFE) or Polyimide give rise to other problems. The coatings typically need to be thicker than the tolerances of the chamber components, necessitating a redesign of some components to enable proper assembly and operation. Thick polymeric coatings also are subject to delamination as a result of gases penetrating tiny holes in the film. Trapped gases then expand and contract during processing and between processing, respectively, prying the film away from the underlying metallic surface. Thermal cycling also stresses the film when the coefficients of thermal expansion of the metal and coating are different. In addition to passive delamination, polymeric coatings typically do not have the physical strength or adhesion characteristics necessary to be used for a dynamic contact, such as a bearing.